Wood preservation



latented Apr. 1, 193d HAROLD W. WALKER, F EDGEWOOD ARSENAL, MARYLANDWOOD PRESERVATION 1T0 Drawing.

Application filed October 26, 1925. Serial No. 65,038.

(GRANTED UNDER THE ACT OF MARCH 3, 1883, AS AMENDED APRIL 30, 1928; 3700. G. 757) The invention described herein may be manufactured and usedby or for the Government for Government purposes, without the payment tome of any royalty thereon.

5' This invention relates to a wood preservative and process of Woodpreservation.

Among the objects of this invention is the provision of a woodpreservative which will afford protection to cut timber against dry rot,decay or attack by destructive organisms.

,A further object of this invention is to provide a wood preservativewhich will not be readily leached from the Wood and which may beincorporated in the wood in sufficient 1 amount to afford protection towood during the economic life of the structure of timber. A furtherobject of this invention is to provide a process whereby thepreservative may be applied to the wood in a cheap, eiiicient and easymanner. A further object of this invention is to provide a processwhereby this impregnation may be carried out in a very cheap, convenientand etficient manner and with the use of cheap and readily availablematerials.

The toxic, antiseptic and preservative properties of AS203 have longbeen known in various industries. AS O is soluble in water at atemperature of 2 C. to the extent of 1.2 parts by weight per 100 partsof solution. At C. it is soluble to the extent of 3 parts per 100 partsof solution. Consequently, when ordinary water is used as the solventfor the As O in a wood preservative, only a small quantity of thispoisonous material will be present and become in-. corporated in thewood. This small quantity is gradually decreased by leaching, due toweather conditions, moisture in the ground and other natural causes, andin a comparatively short time the amount of toxic material remainin inthe wood is insufiicient to prevent deterioration and eventualdestruction of the wood.

I have found that by adding from 25-23% of ammonia to water, that asmuch as 20% of AS 0 can be dissolved therein as As O and NH AsO Iimpregnate the wood with such a solution, and after impregnation theexcess solution is withdrawn from the impregnation vat or tank. Theimpregnated wood is then heated and the excess ammonia and water ispractically all driven oil, leaving the AS203 as such in the pores ofthe wood in such quantity-that the length of time required to leach outa sufiicient amount of toxic material vto leave the Wood withoutsufficient preservative would be greater than the economic life of thetimber structure.

The amount of ammonia that may be ad- .vantageously employed for thisprocess is from 1-4% ofthe solution. It is not advisable to use too muchammonia because the AS203 is highly soluble in an ammoniacal solution of14% and an excess quantity of ammonia has no substantially apparenteffect on the preservative properties of the solution.

In heating the wood after impregnation with the preservative, the excessammonia which is driven oil may be collected in Water and reused forsucceeding batches, and the loss of ammonia by this process may be keptrather low.

Although I prefer to use an ammoniacal solution of AS203, the inventionis not limited thereto but includes 'the use of other ainmoniacalsolutions of arsenic compounds, examples of which are the sulphides ofarsenic, As S ,As S and AS 8 These sulphides are brought into solutionby treating with ammonius hydroxide. A similar eifect is obtained byusing a solution of AS203 in ammonium sulphide.

The present invention is not limited to the specific details set forthin the foregoing ex 8 amples which should be construed as illustrativeand not by way of limitation, and in view of the numerous modificationswhich may be eiiected therein Without departing from the spirit andscope of this invention, i

it is desired that only such limitations be imposed as are indicated inthe appended clalm.

I claim as my invention:

A process for treating wood comprising impregnatin the wood only witharsenic trioxide. carrie in an aqueous solution of ammonia, withdrawingthe excess solution from the wood, heating and drying the impregnatedwood and recovering the ammoma evolved.

HAROLD W. WALKER.

